Cryogenics relates to the production and maintenance of very low temperatures, often using cryogenic fluids such as hydrogen, helium, nitrogen, oxygen, air or methane. Various discussions concerning cryogenic systems can be found in literature. See e.g., Barron, Cryogenic Systems, 2d Ed., Oxford University Press (1985); Bell, Jr., Cryogenic Engineering, Prentice Hall, Inc. (1963); Vance, Cryogenic Technology, John Wiley & Sons, Inc. (1963) and Timmerhaus et al., Cryogenic Process Engineering, Plenum Press (1989).
In addition, U.S. Pat. Nos. 3,320,755; 3,714,796 and 3,728,868 disclose cryogenic refrigeration systems (i.e. cryostats). U.S. Pat. No. 4,237,699 relates to cryostats for producing cryogenic refrigeration by expansion of a working fluid through a Joule-Thomson orifice. The cryostat disclosed in U.S. Pat. No. 4,237,699 can be placed in a dewar so that the liquefied working fluid can be maintained to cool an object such as an infrared detector. Similarly, U.S. Pat. Nos. 3,021,683 and 3,048,021 relate to gas liquefiers. U.S. Pat. No. 4,653,284 discloses a Joule Thomson heat exchanger and cryostat. U.S. Pat. No. 4,781,033 discloses a heat exchanger for a fast cooldown. The above-mentioned devices and apparatus are useful in liquefaction processes.
Air liquefaction is often utilized to provide liquid or gaseous oxygen for chemical processing and steel production plants. The remaining liquid nitrogen is used in food processing plants and the like. Liquid nitrogen is also converted to a gas for use as a protective blanket for reactive elements in chemical plants. Because of transportation costs and other factors, liquefied nitrogen is typically re-gasified after being liquefied in an air liquefaction plant for use in such facilities. As discussed in greater detail herein, the liquefied nitrogen is transported from an air liquefaction plant, a tanker or the like through a pipe line to an evaporator where it is gasified. The gasified nitrogen is then transported to the chemical, steel or food processing plant for use.
The gaseous nitrogen blankets protect reactive elements used in various processing plants where explosion or contamination hazards are a significant concern. In addition, many reactive elements used in these plants will undergo oxidation if not adequately protected. In addition to reducing explosion and contamination hazards, gaseous nitrogen blankets also reduce the possibilities of undesired oxidation. For example, gaseous nitrogen blankets are sometimes employed in plants where chlorine is produced from salt brine by electrochemical methods. Additionally, food processing plants may use gaseous nitrogen during food processing to preserve expensive foods. Liquid nitrogen is used to flash freeze shrimp or foods that cannot be processed with acceptable quality using normal freezing processes.
As mentioned above, prior art techniques for providing gaseous nitrogen blankets to these processing plants typically include the use of air liquefaction plants. In large industrial applications for example, a gas pipe line connects the air plant to the chemical processing plant. The gas pipeline length x is typically about 500-5000 meters. The liquid nitrogen is converted to a gas in an evaporator and transported through the gas pipe line. Heat input requirements to the evaporator must be equivalent to the latent heat of vaporization for the liquid nitrogen, i.e. about 43.6 W/liter/hour.
During the summertime and during periods of high humidity, the liquid nitrogen plant often cannot deliver sufficient gas to the chemical plant. This can be attributed in part to the high humidity causing ice formation on the evaporator. In addition to heat energy requirements to the evaporator, geographical location can thus be a limiting factor in designing such plants. Even if such plants can be constructed in areas where the climate is subject to frequent periods of high humidity, additional design and construction costs must be taken into account to protect the evaporator from the disadvantages associated with such icing.
Another disadvantage associated with the prior art is that separate cooling systems are utilized for power supplies and other large equipment requiring active cooling. For example, in situations where large power supplies are also used in the plant, they are typically either water or air cooled. Consequently, the regulation of nitrogen gas flow from the evaporator is separate from the process requirements in the plant.
It would therefore be desirable to provide methods and apparatus for improving liquid cryogen gasification such that heat energy requirements and disadvantages caused by high humidity environments are reduced, thereby overcoming the shortcomings associated with the prior art. The resulting gasification will also improve the operation of large equipment requiring active cooling.